Method of making composite light-polarizing element

ABSTRACT

A composite light-polarizing lens comprising a light-polarizing element having coated on each surface thereof a layer which enhances adhesion between in situ formed lens components and inhibits migration of lens constituents between said light-polarizing elements and said in situ polymerized components during formation of said lens.

This application is a continuation-in-part of application Ser. No.249,651, filed May 2, 1972, U.S. Pat. No. 3,833,289 which, in turn, is acontinuation-in-part of application Ser. No. 41,504, filed May 28, 1970,now abandoned, the latter a division of application Ser. No. 726,141,filed May 2, 1968, also abandoned, all in the name of Norman W. Schuler.

BACKGROUND OF THE INVENTION

The present invention is particularly directed toward compositelight-polarizing synthetic plastic ethical lenses of the type disclosedin application Ser. No. 41,504, now abandoned, also assigned to PolaroidCorporation. Such lenses are generally adapted to be utilized inproviding substantially any given ophthalmic lens prescription toaccommodate the eyes of a prospective user and facilitate a correctionto such user's vision, while at the same time providing to such user thebenefits which may only be achieved by employing a light-polarizingmaterial.

It will be apparent that many advantages may be achieved by utilizing atough, optical quality plastic material for ophthalmic lenses in lieu ofglass. Plastics are more highly resistant to fracture glass, do notrequire extremely high temperatures to produce a desired lens, and donot generally require the expensive grinding and polishing operationswhich must be carried out, in most cases, before a glass lens iscompleted. Until the advent of modern transparent optical qualitysynthetic plastic materials, it was highly undesirable to form lensesfrom synthetic plastics since most of the available plastics were softand therefore susceptible to severe abrasion. In addition, in thoseinstances where tough, thermosetting resins were utilized for lensmanufacture, such resins were difficult to handle in the thicknessesrequired for ophthalmic lenses. Until the development of the lensesdescribed in the aforenoted application, people requiring correctivelenses to restore and/or aid their vision were denied the benefits oflight-polarizing lenses which were made entirely of synthetic plasticmaterials. The few light-polarizing ethical lenses available comprisedglass elements between a light-polarizing member was interposed.However, this obviously did not eliminate any of the problems inherentin glass lenses and, due to the difficulties encountered in themanufacture of such lenses and the extremely high incidence of rejects,such lenses were inordinately expensive.

As has been claimed in the above-denoted application, the method ofmanufacturing synthetic plastic ophthalmic lenses generally comprisesthe injection of a synthetic plastic monomeric material immediatelyadjacent each side of a light-polarizing element secured into a mold.The respective curvatures of the surfaces of the ultimately producedlens are, of course, governed by the shapes of the surfaces of the moldelements adjacent each respective surface of the light-polarizingelement and offset therefrom a predetermined distance. Since, as will beappreciated from the discussion hereinbelow, plastic ophthalmic lensesare generally ground to a given prescription by grinding only the rearof concave surface of the lens, the light-polarizing element should beoffset toward the convex side of the lens as much as possible therebyproviding a substantially thicker concave in situ polymerized componentthan the convex in situ polymerized component. According to thedisclosure in application Ser. No. 249,550, filed May 2, 1972, alsoassigned to Polaroid Corporation, this may be facilitated by securinginto a resilient mold component a light-polarizing element which hasbeen provided with projections about its periphery to provide suchpredetermined distance between at least one face of the light-polarizingelement and its complementary mold component, although the same resultmay be accomplished by providing a shim of a predetermined thicknessbetween the front mold and the polarizer.

It has been found that, in accordance with the method for manufacturingsynthetic plastic composite light-polarizing lenses disclosed andclaimed in above-denoted application Ser. No. 41,504, under certaincircumstances catalyst utilized with monomeric materials required toform outer lens components of the lenses disclosed therein oftenmigrates from the monomeric materials in which they are contained intothe light-polarizing element which forms an integral component of theultimate lens thereby deleteriously affecting the light-polarizingelement by bleaching dyes comprising the element. In addition,plasticizer components of the light-polarizing element were sometimesfound to migrate therefrom into polymerizing monomer which causes theformation of a "soft" polymeric material generally containing striationsand haze; and monomer sometimes migrated into the light-polarizingelement and caused it to deform and buckle. By the instant invention, acombination tiecoat-barrier layer is provided with obviates themigration effect of catalysts, monomeric materials, and plasticizerswhich are employed in forming the composite lenses of the presentinvention and insures adequate adhesion between the components of thecomposite structure.

OBJECTS OF THE INVENTION

It is accordingly an object of the present invention to providelight-polarizing composite ophthalmic lenses which comprise syntheticplastic materials.

It is another object of the present invention to provide a compositesynthetic plastic light-polarizing lens which includes tiecoat-barrierlayers which prevent migration of plasticizer, catalyst, and monomermaterials from given lens components to other lens components.

It is a further object of the present invention to provide a process forthe production of light-polarizing ophthalmic lenses which iseconomical, has a low incidence of rejects and obviates the migrationproblems heretofore encountered which caused a substantial incidence ofrejects.

The invention accordingly comprises the process involving the severalsteps and the relation of one or more of such steps with respect to eachof the others and the product possessing the features, properties andrelation of elements which are exemplified in the following detaileddisclosure and the scope of the application which will be indicated inthe claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompany drawing wherein:

FIG. 1 is a side, cross-sectional view of the composite light-polarizinglens element of the present invention; and

FIG. 2 is a side cross-sectional view of the lens of the presentinvention being formed in a suitable mold.

DETAILED DESCRIPTION OF THE INVENTION

Stated generally, the present invention contemplates the casting ofplastic lenses in mold cavities formed, preferably, between rigid andflexible mold components, said flexible mold components being preferablycylindrical. More specifically, the invention contemplates theinterposition of a shaped light-polarizing synthetic plastic memberbetween layers of an optical quality synthetic monomeric material in amold comprising resilient and rigid components; and heating the materialand mold thereby causing in situ polymerization of said monomericmaterial with the concomitant formation of a composite synthetic plasticlight-polarizing lens structure -- it being a principal feature of theinvention that the light-polarizing element have a coating on each ofits surfaces which performs the functions of insuring a suitable bondbetween the light-polarizing element and adjacent in situ formed lenscomponents and inhibiting plasticizer migration from thelight-polarizing element into the monomeric materials injected adjacentthereto, while, at the same time, preventing monomer, and catalystcontained in the monomer, from migrating into layers comprising thelight-polarizing element.

The principal lens produced by the present invention is preparedaccording to the procedure generally described above, which will be morefully discussed below, and is supplied to optical laboratories, usuallyin a semi-finished form, for distribution. Due to limitations in moderngrinding and polishing equipment for plastics, the front, or convexsurface of the lens is preferably cast into its finished configurationat the time of manufacture, its surface requiring no grinding orpolishing. The concave surface, however, is preferably formed in avariety of diopters which encompass a range of plus and minuscorrections. Any given particular prescription may be prepared byselecting a lens with cast-in optics close to the prescribed dimensions,followed by grinding and polishing the concave surface according to theexact prescription required. It will be evident that in certaininstances the configuration of the lens will conform to the desiredprescription without further grinding or polishing.

As is well known in the lens casting art, as polymerization occurs, thelens material shrinks a certain degree, thereby, in many instances,causing the lens surfaces to conform to a shape different from that ofthe mold surfaces. There are numerous well-known techniques available tothe operator to provide a hedge against this phenomenon. One techniqueis to dilute the monomer mix with a soluble polymer such as, forexample, polymethyl methacrylate. The preferred technique is toconstruct the body of the mold of a resilient material, and preferably avinyl material which will shrink in conjunction with the shrinkageinherent in the polymerization process, thus assuring substantialconformity of the ultimate configuration produced on each of the lenssurfaces with the surface of the rigid mold element with which it isintimate.

Any suitable polymeric light-polarizing sheet material which willproduce the desired light-polarization effect may be utilized in thecontext of the present invention. Excellent results have been obtainedusing a transparent sheet of oriented polyvinyl alcohol containing adichroic dye. The manufacture and utilization of such sheet material maybe appreciated with reference to U.S. Pat. Nos. 2,237,567 and 2,554,850,incorporated herein by reference. Among other materials which may beutilized as light-polarizing elements in the present invention are, forexample, polyvinyl butyral and polyvinyl alcohol containingsubstantially oriented molecules of dehydrated polyvinyl alcohol andderiving its light-polarizing properties essentially from the dehydratedmolecules. The manufacture and utilization of the last-named sheetmaterial may be appreciated with reference to U.S. Pat. Nos. 2,173,304;2,255,940; 2,306,108; 2,445,555; 2,453,186; and 2,674,159, allincorporated herein by reference.

In a preferred embodiment of the present invention, the light-polarizingmaterial is sandwiched between relatively thin layers of an opticalquality transparent polymeric material which serves to support saidlight-polarizing material. Among the materials which may be utilized forthis purpose are cellulose acetate butyrate, cellulose acetate,cellulose triacetate, etc. Cellulose acetate butyrate is preferred. Thebond between the light-polarizing element and the polymeric supportmaterial may be accomplished, for example, according to the methods ofBuzzell and Bloom, U.S. Pat. Nos. 3,620,888 and 3,588,216, respectively,both incorporated herein by reference. It will be appreciated from areading of the above patents that lamination of a cellulose acetatebutyrate support material to a typical polarizing sheet as, for example,one comprising polyvinyl alcohol, may be accomplished either bysubcoating the cellulose acetate butyrate material with a suitablecompound such as, for example, cellulose nitrate, and then laminatingthe subcoated material to the polyvinyl alcohol light-polarizing sheetusing a well-known pressure roll technique with a typical adhesive forsuch materials such as, for example, a two percent polyvinyl alcoholsolution, or alternatively, the lamination may be accomplished by thepartial conversion of the surface of the cellulose acetate butyrate tocellulose, subcoating the surface with polyvinyl alcohol, and pressurelaminating the subcoated cellulose acetate butyrate to thelight-polarizing material, as more fully disclosed in the Buzzell patentmentioned above.

In the most preferred embodiment of the present invention, thetiecoat-barrier layers employed to prevent the migration of variousmaterials from the light-polarizing element to adjacent injectedmonomeric components, and concomitantly from such monomeric componentsto the light-polarizing element, are preferably coated onto, forexample, the cellulose acetate butyrate polymeric support material forthe light-polarizing element on the surface thereof opposed to itssurface which is laminated directly to the light-polarizing element.This may be accomplished prior to lamination of such material to thelight-polarizing element by employing, for example, a conventional slotcoater which provides a film of a thickness between 1 and 20 microns.While numerous materials may be obvious to those of ordinary skill inthe art which will provide the denoted functionality in the context ofthe present invention, the materials utilized will preferably containnitrocellulose having a viscosity measured by ASTMD301-56 of higher than600 sec. and preferably higher than 2500 sec. and having a nitrogencontent of about twelve percent. The coating material should preferablycontain more than twenty percent nitrocellulose based upon the weight ofthe total resins in the coating material. While the tiecoat-barrier ofthe present invention may comprise 100 percent nitrocellulose which isessentially completely crosslinked by a crosslinking agent, as, forexample, an organic titanate, it will preferably comprise at least oneother resinous material which contributes a high degree ofimpenetrability by the components present during the formation of thelenses of the present invention. Among such material are, for example,phenolics, e.g., melamine formaldehyde, urea formaldehyde, phenolformaldehyde; polyhalogenated vinyls, e.g., polyvinyl chloride,polyvinylidene chloride; polyvinyl esters and acetals, e.g., polyvinylacetate, polyvinyl butyrate; polyamides, e.g., soluble nylons;polyacrylates, e.g., polyacrylonitrile, polyethylene glycoldimethacrylate; soluble poly ester resins; epoxy resins; etc. Thepreferred material for use in the context of the present invention is amelamine formaldehyde-urea formaldehyde resinous material.

The light-polarizing element employed in fabricating the compositelenses of the present invention is preferably preformed to adequatelyconform to the respective configurations of the plastic elements whichare to be polymerized on either side thereof. Accordingly, it will beapparent that the more extreme configurations in the convex and concaveelements will require concomitant deviations in the shape of thelight-polarizing element from the planar configuration. In addition, inorder to avoid light refraction problems the curvature of thelight-polarizing element should be approximately the same as thecurvature of the convex surface of the lens. In order to preventinjuring the light-polarizing element during grinding and polishing ofthe concave surface, the light-polarizing element should be situatedreasonably close to the convex surface of the lens. Preforming of thelight-polarizing element is preferably accomplished by a coventionalpressing operation.

During the preforming of the light-polarizing insert, it will beappreciated that various diopters of curvature may be employed and, asdenoted, such curvatures will generally conform to the desired curvaturethat the outer or generally convex surface of the ultimate lens willfollow.

In actual operation, a suitable catalyst is dissolved in the monomericmaterial from which the outer layers of the desired lens are to bemanufactured. The mold, as depicted in FIG. 1 is preferably constructedwith outer rigid mold elements, preferably comprising glass, the frontelement being seated against raised means depending from alight-polarizing member which has coated on each face thereof atiecoat-barrier as discussed hereinabove, and is secured in place by aresilient body element constructed, for example, of rubber. Theresilient mold element is preferably cylindrical; however, within thecontext of the present invention it may assume any desired transversecross-sectional configuration, as, for example, rectangular, square,elliptical, etc. Using a suitable syringe, monomer with catalystincorporated therein is injected through the resilient area into themold on one or both sides of the light-polarizing element, and theentire structure is then heated for a sufficient time to cause thematerial to polymerize. Any optical quality synthetic plastic materialmay be utilized for the outer members of the lenses of the instantinvention provided, however, that its ultimate second order transitiontemperature is above the highest temperature at which the lenses may beutilized; as, for example, in the average usage of ophthalmic lenses,130° F. Exemplary monomeric materials are 1,3-butylene glycoldimethacrylate, allyl methacrylate, trimethylol propane triacrylate,cyanoethyl methacrylate, bis phenyl A dimethacrylate, methoxybutylmethacrylate, methyl methacrylate, diethylene glycol bisallyl carbonate,ethoxymethyl methacrylate, ethylene glycol dimethacrylate, ethyleneglycol diacrylate, polyethylene glycol dimethacrylate, etc. Thepreferred material is diethylene glycol bisallyl carbonate. (CR-39 ofPittsburgh Plate Glass Corporation.)

Monomeric materials, such as those enumerated in the paragraph nextabove, may be formed into homopolymers, mixed with polymers to reduceshrinkage or, copolymerized with materials which increase theirhardness, heat resistance, etc. Among such materials which may becopolymerized with the above-mentioned exemplary monomers are vinylacetate, maleic anhydride, ethylene glycol maleate, triallyl cyanurate,diallyl phthalate, methyl methacrylate, etc.

In the event the monomer is injected on only one side of the securedlight-polarizing element, the light-polarizing element will bepreferably provided with, close to its periphery, one or more holes inorder to facilitate transfer of monomeric material from the cavity intowhich it has been injected into the opposed cavity. Since, as has beenaforenoted, the concave area of the lens will comprise a substantiallythicker polymerized section, the polymer will preferably be injectedinto that cavity and will flow therefrom into the convex area. Accurateamounts of material for injection may be determined by simple volumetriccomputations. In addition, suitable air escape ports may be provided ina conventional manner.

Since thermosetting materials are, as a rule, far more abrasionresistant than thermoplastic materials, they are preferred for use inthe present invention. It has been found that when diethylene glycolbisallyl carbonate, the preferred material, is utilized, a cure time ofabout eight to sixteen hours is required before the lens is completelyformed.

Any catalyst compatible with the chosen monomeric material utilized inthe present invention may be employed. Examples of suitable catalystsare diisopropyl percarbonate, benzoyl peroxide, azobisisobutyronitrile,methylethyl ketone peroxide, di-s-butyl percarbonate, etc. In thepreferred systems of the present invention, di-s-butyl percarbonate hasbeen found to give extremely fine results when utilized in proportionsof approximately 2.5 to 4.5 percent based upon the weight of themonomer.

In order to provide a desired color to the lenses of the presentinvention, various dyes may be incorporated therein either by beingabsorbed on the surface of the outer polymeric material by beingintegral with the initial monomeric charge, or by being imbibed or castinto the plastic support members for the light-polarizing material. Inaddition, other agents such as ultraviolet radiation absorbers, infraredradiation absorbers, visible light attenuation dyes, etc., may be addedto the system to provide additional benefits.

Referring to FIG. 1 of the drawing, there is illustrated a cut-away viewof a typical lens structure of the present invention. Elements 2 and 3with concave and convex external surfaces, respectively, comprisepolymeric material which has been polymerized in situ in contact withpreformed light-polarizing element composite structure 1 which compriseslight-polarizing element 4, transparent plastic elements 5 which act assupports for element 4 and thin coatings of tiecoat-barrier material 6.

Referring now to FIG. 2, elements 1, 2 and 3 are depicted in mold 11which is composed of a resilient body component 8 and rigid elements 6and 7. Rigid element 6 which will provide the convex surface to theultimately produced lens is in direct contact with projections 9provided according to application Ser. No. 249,550. The assembled moldis securely held together by clamp element 10; however, it should beunderstood that any suitable means of holding the mold together such as,for example, integral resilient element lip members, etc., may beutilized. The resinous material injected between the light-polarizingcomposite element 1 and elements 6 and 7, respectively, may be insertedinto the mold in any known manner, but preferably by injection into theconcave cavity through the resilient mold member with consequenttransfer of monomeric material to the convex cavity by means of suitablemonomer transfer ports 12 which provide communication between therespective convex and concave cavities of the assembledmold-light-polarizing structure. While the resilient portion of the moldmay generally comprise any elastomeric material, it is preferred toemploy a resilient mold member comprising polyvinyl chloride plasticizedwith dioctyl phthalate in conventional manner. See, for example, thedisclosure of application Ser. No. 249,549, also assigned to PolaroidCorporation.

The plastic lenses of the present invention may be produced as afinished blank, or so-called "uncut lens" or as an unfinished form, aso-called semi-finished lens, which may subsequently be ground andpolished, if necessary, using the same technology and major equipmentutilized on crown glass. However, as has been alluded to above, in theevent that grinding and polishing is performed, the operations willpreferably be carried out on the concave surface of the lens, since, inthe preferred embodiments, nearly the full range of possibleprescriptions will have been cast into the convex surfaces of lensesfrom which the operator may choose. It is estimated that in order tofully accomplish this goal, between four and five hundred differentconvex configurations will be utilized in producing a full range oflenses for ophthalmic use. While the primary purpose of the presentinvention is to provide ethical ophthalmic lenses, it will, of course,be appreciated that lenses cast in a plano configuration for use withoutalteration is anticipated herein.

The following example illustrates the preparation of a typical lens ofthe instant invention and is to be considered illustrative only and nottaken in a limiting sense.

EXAMPLE

A sheet of a light-polarizing material comprising oriented polyvinylalcohol stained with a dichroic dye (H-sheet), each face of which hasbonded thereto a layer of cellulose acetate butyrate of fromapproximately 5 mils to approximately 14 mils in thickness -- saidcellulose acetate butyrate layers having integral therewith alight-attenuating dye material -- is provided. Each exposed surface ofcellulose acetate butyrate has slot-coated thereover a layerapproximately 2 microns in thickness comprising the polymerizationproduct resultant from coating onto such surface a compositioncomprising:

    Acetone            8400.0     cc.                                             Methanol           11000.0    cc.                                             Methylcellosolve   600.0      cc.                                             Nitrocellulose [Hercules                                                      RS-4000-5000 sec. nitro-                                                      cellulose (high molecular)]                                                                      220.0      gms.                                            duPont Tyzor AA [titanium                                                     di (acetyl acetonate)]                                                                           8.5        gms.                                            Rohm & Haas U-Formite Mu-56                                                   (melamine formaldehyde/urea                                                   formaldehyde resin)                                                                              80.0       gms., and                                       Maleic Acid        4.0        gms.                                        

The maleic acid is a polymerization catalyst for the melamineformaldehyde resin and the titanium di (acetyl acetonate) is acrosslinking agent for the nitrocellulose. The acetone, methanol andmethylcellosolve are solvents which evaporate after coating. Thepolarizer, having a tiecoat-barrier on each side thereof, is thenpressed to a spherical configuration of approximately 6 diopters betweenheated platens, and cut into a circular configuration whilesimultaneously having projections raised about the periphery thereof andtwo small holes placed opposed to one another generally along theperiphery thereof. The hole-providing functionality and projectionraising is generally facilitated by means of a conventional die memberwhich provides such facility commensurate with the cutting operation.The formed light-polarizing element is then placed onto a flange of acylindrical resilient mold component and an upper glass mold element isplaced in contact with the raised projections on the convex surface ofthe light-polarizing element, the surface configuration of the glassmold element substantially opposed to the surface of thelight-polarizing element conforming to the surface configuration of saidlight-polarizing element. A second glass mold element is placed inabutting relationship to said resilient mold element on the side of saidlight-polarizing element opposed to the first rigid mold element and theentire unit is clamped together in conventional fashion. About 3 1/2percent, by weight, of di-s-butyl percarbonate catalyst is added to apredetermined quantity of diethylene glycol bisallyl carbonate monomer,purchased from Pittsburgh Plate Glass Company under the tradedesignation CR-39, and injected through the resilient mold componentinto the concave cavity (adjoins concave surface of light-polarizingelement) utilizing a suitable syringe. The unit is then placed in anoven for 15 hours where the temperature is raised from 90°F. toapproximately 160°F. in conventional manner. After approximately a15-hour cure time, the mold is disassembled, and the composite lens isremoved and preferably placed in an annealing oven at 200° F. for about2 hours to relieve any stresses which may have been built up during theforming cycle.

The instant invention contemplates, at the option of the operator, theutilization of conventional additives which may accelerate, inhibit orotherwise alter the polymerization characteristics of the chosen polymerin order to achieve the desired cure cycle for the lens disclosedherein.

Throughout the specification, the term "ethical" has been used todescribed certain ophthalmic lenses. In the context of the presentinvention, "ethical" denotes lenses of the nonplanar variety, which areproduced according to a given prescription.

Since certain changes may be made in the above product and processwithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. The method of manufacturing synthetic plasticlight-polarizing ophthalmic lens which comprises:applying as acontinuous coating on each surface of a light-polarizing element a layerwhich enhances adhesion between said light-polarizing element andsubsequently in situ polymerized lens components and significantlyinhibits migration of lens constituents to said light-polarizing elementduring polymerization; securing said coated light-polarizing elementinto a mold; providing a continuous layer of a synthetic plasticmonomeric material over the entire surface of each side of saidlight-polarizing element which will comprise the light transmission areaof the ultimately formed lens; and causing said monomeric material topolymerize thereby forming a composite light-polarizing ophthalmic lens.2. The invention of claim 1 wherein said continuous coating comprisescrosslinked nitrocellulose.
 3. The invention of claim 2 wherein saidcoating additionally comprises a melamine formaldehyde condensationpolymer.
 4. The invention of claim 3 wherein said melamine formaldehydecondensation polymer is a melamine/urea-formaldehyde condensationpolymer.